With the advances in chip materials and corresponding fabrication technologies, microfluidics chip has been used in many important new functions and become enabling tools in various fields of research. The conventional strategy for fabricating microfluidic chips involves two steps: generating channel structures in a flat substrate, and sealing of the channels with a roof. This strategy is first employed to fabricate silicon and glass microfluidic chips with photolithographic technologies used in the semiconductor industry. The conventional methods are costly (tens to hundreds of dollars per chip), but resistant to heat and solvents, and could produce very small channels when silicon is used. Subsequently, polymer-based microfluidic chips are developed, using polydimethylsiloxane (PDMS), poly (methyl methacrylate) (PMMA), polycarbonate (PC), polyethylene (PE), polyimide, polystyrene, poly(vinyl chloride), cyclic olefin copolymer and hydrogels, which simplify the fabrication process, reduce the cost of production, and extend the functions of devices, e.g., on-chip valve control and cell culture. Accordingly, different microfabrication techniques are used, such as replica molding, injection molding, thermoforming and hot-embossing. These devices have become important new tools in various research fields; however, the two-step fabrication strategy inherently raised the cost and limited the throughput of production, e.g., the bonding of polymer chips is normally accomplished with oxygen plasma treatment, nanometer-thick glue layer, dissolving solvent, or melt-bonding, et al.
Besides the two-step fabrication strategy, there are also single-step strategies reported, which make fabrication of 3D microchannel structures possible. For example, one way is to use sacrificial templates to determine the internal shape of the channels. But the removal of the templates is normally time-consuming and often involves organic solvents or extreme conditions such as high temperature. 3D printing has been employed as another single-step fabrication strategy, but it is still costly and unsuitable for large scale production because of the relatively slow printing speed.
While the aforementioned methods have found numerous applications in research laboratories, few commercial products have been launched, mainly obstructed by the cost of fabrication, reliability of devices for use and storage, as well as the apparatus needed for operating the system. With regards to the demand of cost-effective devices for commercial applications, some smart designs of paper based microfluidic devices have been reported. Because paper can hold water in it, simply printing hydrophobic materials onto certain area of a piece of paper, the remaining area on the paper can serve as microfluidic channels without the need of sealing the channel roof. This strategy is very useful for bioassays that require passive pumping; nevertheless, it sometimes faces problems of sample retention and limited feature resolution, and the roof-less channels are less suitable for certain applications involving heating, volatile solvents, or particles/droplets/beads, etc. In addition, it is not easy to manufacture on-demand valving and pumping on chip. For such applications, a solution to produce affordable microfluidic devices is still in high demand.
When considering the possibility of any new strategy to fabricate microfluidic devices in a really fast and cost-efficient manner, the inventors were attracted by the methods for commercial production of plastic bags for packaging foods, and that for sealing documents using plastic covers. The former uses flexible plastic films, e.g., PE, and the latter uses rigid plastic films, e.g., EVA coated PET; but both employ a hot press to bond the two membranes at the boundary, which only takes a few seconds. Interested by the extremely high speed and low cost of such processes, the inventors did some preliminary attempts to see if a similar strategy could be introduced for the fabrication of microfluidic devices. Unfortunately, the adoption of either strategy was unsuccessful; however, the attempts inspired the inventors to create a new strategy. Interestingly, the inventors found that the combination of a soft film and a rigid film, with the help of a special stamp for heat bonding, generate microchannels as the soft film rises up when being heated, allowing the fabrication of microchannels in a single hot-pressing step, with the speed and cost just like those to seal a plastic bag. The mechanism of this fabrication strategy is different from the previously reported strategies for fabricating microchannels, e.g., hot-embossing, thermoforming, etc.
Herein the inventors describe a novel method for manufacturing microfluidic chips, which is super-fast (within 12 seconds per piece) and extremely cost-effective (less than $0.02 per piece). Different from the conventional two-step strategy for fabricating sealed microchannels, the present application provides a method that generates microchannels in a single step.
It is an object of the present invention to provide an ultra-fast, extremely cost-effective, and environmental friendly method for fabricating flexible microfluidic chips with plastic membranes.
Citation or identification of any reference in this section or any other section of this application shall not be construed as an admission that such reference is available as prior art for the present application.